This application is based on Japanese Patent Applications HEI 11-231999 and HEI 11-232000 filed on Aug. 18, 1999, all the contents of which are incorporated herein by reference.
a) Field of the Invention
The present invention relates to a solid state image pickup device, and more particularly to a solid state image pickup device whose adjacent pixels are disposed shifted by a half pitch between pixels in both vertical and horizontal directions, and to its read method.
b) Description of the Related Art
High integration of pixels has been desired for a solid state image pickup device such as a CCD solid state image pickup device.
FIG. 18 is a plan view of a general interline type CCD solid state image pickup device.
The solid state image pickup device is formed on a semiconductor substrate 201 made of, for example, silicon.
A CCD solid state image pickup device X formed on the semiconductor substrate 201 includes pixels 203, vertical charge transfer paths 205, a horizontal charge transfer path 207 and an output amplifier 211. A plurality of pixels 203 are regularly disposed on the semiconductor substrate 201 in the vertical and horizontal directions.
Each pixel 203 includes a photodiode (photoelectrical conversion element) 203a and a read gate (transfer gate) 203b. The photodiode 203a converts incident light into electric charges and stores the electric charges. The transfer gate 203b reads the electric charges stored in the photodiode 203a to the vertical charge transfer path 205.
Each pixel column P11 constituted of a plurality of pixels 203 disposed in the vertical direction is provided with one vertical charge transfer path 205. The vertical charge transfer path 205 is made of, for example, an n-type conductive layer formed on the semiconductor substrate 201. The horizontal charge transfer path 207 is disposed at the lower ends of the vertical charge transfer paths 205.
The horizontal charge transfer path 207 is constituted of mainly an n-type conductive layer 208 in the semiconductor substrate 201 and horizontal charge transfer electrodes 221 made of two polysilicon layers (first and second polysilicon layers) formed on the semiconductor substrate 201.
The n-type conductive layer 208 includes high concentration regions 208a having a high n-type impurity concentration and low concentration regions 208b having a low n-type impurity concentration formed alternately. The high concentration region 208a forms a potential well having a low potential energy. The low concentration region 208b forms a potential barrier having a high potential energy. Potential barriers and potential wells are alternately disposed in the horizontal direction. Two pairs of one potential barrier and one potential well form one charge transfer packet (hereinafter simply called a xe2x80x9cpacketxe2x80x9d). A number of packets are formed along the horizontal direction.
First polysilicon layer electrodes (horizontal transfer electrodes 221-1, 221-3, 221-5, . . . , refer to FIG. 19) are formed on the high concentration regions 208a (potential wells), and second polysilicon layer electrodes (horizontal transfer electrodes 221-0, 221-2, 221-4, . . . , refer to FIG. 19) are formed on the low concentration regions 208b (potential barriers).
The horizontal charge transfer electrodes 221-0 and 221-1 are connected together and a voltage xcfx861 is applied to these electrodes. The horizontal charge transfer electrodes 221-2 and 221-3 are connected together and a voltage xcfx862 is applied to these electrodes. Similarly, the horizontal charge transfer electrode 221-4 and 221-5 are connected together and the voltage xcfx861 is applied to these electrodes.
As shown in FIG. 19, two vertical charge transfer electrodes 215, e.g., vertical charge transfer electrodes 215-1 and 215-2, are formed on the vertical charge transfer path 205 in a space between adjacent pixels disposed in the row direction.
Voltages V1 to V4 are applied to the vertical charge transfer electrodes 215-1, 215-2, 215-3 and 215-4. Similarly the voltages V1 to V4 are applied to the vertical charge transfer electrodes 215-5 to 215-8, and 215-9 to 215-12. The voltages V1 to V4 are, for example, 0 V for forming a potential barrier in the vertical charge transfer path, 8 V for forming a charge transfer potential well, and 15 V for reading electric charges from pixels.
The vertical charge transfer path 205 is electrically connected to one potential well region of each packet of the horizontal charge transfer path 207.
The operation of the solid state image pickup device will be described with reference to FIGS. 18 and 19.
When V1 is set to 15 V, electric charges stored in all the photodiodes 203a connected to the V1 vertical charge transfer electrodes are read via the transfer gates 203b to the vertical charge transfer paths 205.
A relatively low plus voltage, e.g., 8 V, is applied to the vertical charge transfer electrode 215-1, and also to the vertical charge transfer electrodes 215-2 and 215-3. Then, the voltage at the vertical charge transfer electrode 215-1 is reset to 0 V and a voltage of 8 V is applied to the vertical charge transfer electrode 215-4. These operations are repeated to transfer electric charges in the vertical charge transfer path 205 toward the horizontal charge transfer path by a four-phase driving method.
As a relatively low plus voltage, e.g., 8 V, is used as V1, V2 nd V3, and 0 V is used as V4, the read electric charges distribute under three vertical charge transfer electrodes at V1, V2 and V3.
As V1 is reset to 0 V, the electric charges are confined under the electrodes at V2 and V3. As V4 is set to 8 V, the electric charges distribute under the electrodes at V2, V3 and V4. By repeating this operation, the electric charges are transferred in the vertical charge transfer path 205 toward the horizontal charge transfer path by the four-phase driving method.
As the voltage xcfx861 of the horizontal charge transfer path is set, for example, to 0 V and the voltage xcfx862 to 8 V, electric charges under the xcfx861 electrode are transferred to the region under the right side xcfx862 electrode. At this time, a potential barrier is formed in the left region of the region under the xcfx861 electrode to prevent a counterflow of the electric charges.
Electric charges can therefore be transferred in the horizontal charge transfer path 207 by a two-phase driving method without a mixture of pixels.
With the two-phase driving method using the voltages xcfx861 and xcfx862, electric charges can be transferred in the horizontal charge transfer path 207.
With the above operations, electric charges can be read from pixels of each line connected to the V1 vertical charge transfer electrode.
Next, electric charges are read from pixels on other rows by a similar method. After electric charges of all pixels for V1 are read, a read pulse is used as V2 to read electric charges from pixels connected to the V2 vertical charge transfer electrodes. Similarly, electric charges are sequentially read from pixels connected to the V3 and V4 vertical charge transfer electrodes.
Electric charges transferred to the horizontal charge transfer path 207 are transferred to the output amplifier 211, for example, by the two-phase driving method. The output amplifier 211 amplifies the electric charges and outputs image signals to the external.
By disposing photodiodes 203a two-dimensionally, signals of a two-dimensional image can be obtained.
In order to meet the requirements of high integration of pixels, it is necessary to make the pixel size fine.
With the solid state image pickup device X described above, one vertical charge transfer path 205 is provided for each pixel column P11. Four horizontal charge transfer electrodes 208a, 208b, 208a and 208b are required in order to transfer electric charges transferred from one vertical charge transfer path 205 to the horizontal charge transfer path 207, to the region of the horizontal charge transfer path 207 connected to the next adjacent vertical charge transfer path 205.
If a pixel 203 is made fine to about 2 to 3 micron square, it becomes difficult to perform fine pattering of horizontal charge transfer electrodes 221. Moreover, as the pixel 203 is made fine, the area of the photoelectric conversion element 203a, e.g., a photodiode, becomes small and the amount of accumulated electric charges reduces. Therefore, a dynamic range cannot be made large.
Still further, as the total number of pixels of a solid state image pickup device increases, it takes a longer time to read image signals of one frame.
A general digital camera has an image signal frame rate of {fraction (1/30)} second in the National Television System Committee (NTSC) system.
Even if a time to read image signals of a still image picked up with a digital camera is prolonged, there is no serial problem.
A moving image is displayed on a monitor display of a digital camera in real time. In this case, as the number of pixels increases, it becomes difficult to follow the frame rate. If the number of pixels exceeds one million, it is difficult to read image signals from all pixels in {fraction (1/30)} second. A clear image cannot be obtained.
It is an object of the present invention to provide a solid state image pickup device capable of providing a high pixel density while mitigating a patterning precision of horizontal charge transfer electrodes.
It is another object of the present invention to provide a solid state image pickup device capable of displaying a clear moving image to be monitored and its control method.
According to one aspect of the present invention, there is provided a solid state image pickup device comprising: a plurality of pixel groups disposed on a two-dimensional plane defined by horizontal and vertical directions, the plurality of pixel groups being juxtaposed in the horizontal direction, each of the pixel groups including a first pixel column and a second pixel column, the first pixel column including a plurality of pixels regularly disposed at a first pixel pitch in the vertical direction, the second pixel column including a plurality of pixels regularly disposed at a half pitch of the first pixel pitch in the vertical direction relative to the first pixel column, the second pixel columns being disposed in the horizontal direction at a half pitch of a second pixel pitch of pixels of adjacent first pixel columns of the pixel groups; a first separation region formed between pairs of the pixel groups adjacent in the horizontal direction; a single vertical charge, transfer path extending in the vertical direction and weaving between the first and second pixel columns of each of the pixel groups; and a horizontal charge transfer path formed at one ends of a plurality of vertical charge transfer paths for receiving electric charges transferred from the vertical charge transfer paths and transferring the electric charges in the horizontal direction.
According to another aspect of the present invention, there is provided a method of reading a solid state image pickup device, the solid state image pickup device comprising: a plurality of pixel groups disposed on a two-dimensional plane defined by horizontal and vertical directions, the pixel groups being juxtaposed in the horizontal direction, each of the pixel groups including a first pixel column and a second pixel column, the first pixel column including a plurality of pixels regularly disposed at a first pixel pitch in the vertical direction, the second pixel column including a plurality of pixels regularly disposed at a half pitch of the first pixel pitch in the vertical direction relative to the first pixel column, the second pixel columns being disposed in the horizontal direction at a half pitch of a second pixel pitch of pixels of adjacent first pixel columns of the pixel groups; a first separation region formed between pairs of the pixel groups adjacent in the horizontal direction; a single vertical charge transfer path extending in the vertical direction and weaving between the first and second pixel columns of each of the pixel groups; and a horizontal charge transfer path formed at one ends of a plurality of the vertical charge transfer paths for receiving electric charges transferred from the vertical charge transfer paths and transferring the electric charges in the horizontal direction, wherein: the pixel includes a photoelectric conversion element formed in an area defined by four oblique sides slanted relative to the horizontal and vertical directions; the first separation region is formed along a first set of right or left oblique sides among the four oblique sides of the pixel in the first pixel column; a first read gate is formed near the vertical charge transfer path along one of a second set of upper and lower oblique sides on a side opposite to a region where the first separation region is not formed, and a second separation region is formed along the oblique side where the first read gate is not formed; the first separation region is also formed along a second set of two oblique sides among the four oblique sides of the pixel in the second pixel column on a side opposite to the first pixel column; a second read gate is formed near the vertical charge transfer path along one of a fourth set of two oblique sides not facing the first read gate of the pixel in the first pixel column and on a side opposite to a region where the first separation region is formed, and a third separation region is formed along the oblique side on a side where the second read gate is not formed; and a plurality of vertical charge transfer electrodes are formed extending in the horizontal direction, each of the vertical charge transfer electrodes being formed between pixels of a first pixel row regularly disposed in a row direction and included in the first pixel column and pixels of a second pixel row adjacent to the first pixel row in the vertical direction and regularly disposed in the row direction, the method comprises: a first field output step including a step of reading electric charges from the pixels in a first field to the vertical charge transfer paths by applying read pulses to the vertical charge transfer electrodes at an n-th row and every predetermined rows and a step of transferring the electric charges in the vertical charge transfer paths toward the horizontal charge transfer path by sequentially applying a voltage to the vertical charge transfer electrodes, and transferring the electric charges transferred to the horizontal charge transfer path and outputting the electric charges to an external; a second field output step including a step of reading electric charges from the pixels in a second field to the vertical charge transfer paths by applying read pulses to the vertical charge transfer electrodes at an (n+1)-th row and every predetermined rows and a step of transferring the electric charges in the vertical charge transfer paths toward the horizontal charge transfer path by sequentially applying a voltage to the vertical charge transfer electrodes, and transferring the electric charges transferred to the horizontal charge transfer path and outputting the electric charges to the external; and a third field output step including a step of reading electric charges from the pixels in a third field to the vertical charge transfer paths by applying read pulses to the vertical charge transfer electrodes at an (n+2)-th row and every predetermined rows and a step of transferring the electric charges in the vertical charge transfer paths toward the horizontal charge transfer path by sequentially applying a voltage to the vertical charge transfer electrodes, and transferring the electric charges transferred to the horizontal charge transfer path and outputting the electric charges to the external, wherein the first to third fields are different fields of the solid state image pickup device.
A solid state image pick up device, further comprising a driver circuit for independently applying a voltage to each of a set of eight vertical charge transfer electrodes adjacent in the vertical direction among the plurality of vertical charge transfer electrodes; a horizontal charge transfer path formed at one ends of a plurality of the vertical charge transfer paths for receiving electric charges transferred from the vertical charge transfer paths and transferring the electric charges in the horizontal direction; and an output amplifier formed at one end of the horizontal charge transfer path for amplifying electric charges supplied from the horizontal charge transfer path and outputting to an external is preferable.
According to another aspect of the present invention, there is provided a method of reading a solid state image pickup device, the solid state image pickup device comprising: a plurality of pixel groups disposed on a two-dimensional plane defined by horizontal and vertical directions, the pixel groups being juxtaposed in the horizontal direction, each of the pixel groups including a first pixel column and a second pixel column, the first pixel column including a plurality of pixels regularly disposed at a first pixel pitch in the vertical direction, the second pixel column including a plurality of pixels regularly disposed at a half pitch of the first pixel pitch in the vertical direction relative to the first pixel column, the second pixel columns being disposed in the horizontal direction at a half pitch of a second pixel pitch of pixels of adjacent first pixel columns of the pixel groups; a first separation region formed between pairs of the pixel groups adjacent in the horizontal direction; a single vertical charge transfer path extending in the vertical direction and weaving between the first and second pixel columns of each of the pixel groups; a plurality of vertical charge transfer electrodes formed extending in the horizontal direction, each of the vertical charge transfer electrodes being formed between pixels of a first pixel row regularly disposed in a row direction and included in the first pixel column and pixels of a second pixel row adjacent to the first pixel row in the vertical direction and regularly disposed in the row direction; a driver circuit for independently applying a voltage to each of a set of eight vertical charge transfer electrodes adjacent in the vertical direction among the plurality of vertical charge transfer electrodes; a horizontal charge transfer path formed at one ends of a plurality of the vertical charge transfer paths for receiving electric charges transferred from the vertical charge transfer paths and transferring the electric charges in the horizontal direction; and an output amplifier formed at one end of the horizontal charge transfer path for amplifying electric charges supplied from the horizontal charge transfer path and outputting to an external, wherein: the pixel in the first pixel column is a first color pixel including a photoelectric conversion element and a first color filer; and the pixels in the second pixel column comprise a second color pixel including a photoelectric conversion element and a second color filer and a third color pixel including a photoelectric conversion element and a third color filer, the second and third color pixels being alternately disposed in the vertical direction and in the horizontal direction, the method comprises: a) a step of reading electric charges to the vertical charge transfer paths by sequentially applying a read pulse to the first to eighth vertical charge transfer electrodes so as to read the electric charges of a same color from a same vertical charge transfer path; b) a step of transferring the electric charges read to the vertical charge transfer paths toward the horizontal charge transfer path; c) a step of transferring the electric charges read to the horizontal charge transfer path toward the output amplifier; d) amplifying the electric charges supplied from the horizontal charge transfer path and outputting the electric charges to the external; and e) repeating the steps a) to d) for pixels of different rows to read electric charges from all the pixels.
According to another aspect of the present invention, there is provided a method of reading a solid state image pickup device, the solid state image pickup device comprising: a plurality of pixel groups disposed on a two-dimensional plane defined by horizontal and vertical directions, the pixel groups being juxtaposed in the horizontal direction, each of the pixel groups including a first pixel column and a second pixel column, the first pixel column including a plurality of pixels regularly disposed at a first pixel pitch in the vertical direction, the second pixel column including a plurality of pixels regularly disposed at a half pitch of the first pixel pitch in the vertical direction relative to the first pixel column, the second pixel columns being disposed in the horizontal direction at a half pitch of a second pixel pitch of pixels of adjacent first pixel columns of the pixel groups; a first separation region formed between pairs of the pixel groups adjacent in the horizontal direction; a single vertical charge transfer path extending in the vertical direction and weaving between the first and second pixel columns of each of the pixel groups; a plurality of vertical charge transfer electrodes formed extending in the horizontal direction, each of the vertical charge transfer electrodes being formed between pixels of a first pixel row regularly disposed in a row direction and included in the first pixel column and pixels of a second pixel row adjacent to the first pixel row in the vertical direction and regularly disposed in the row direction; a driver circuit for independently applying a voltage to each of a set of eight vertical charge transfer electrodes adjacent in the vertical direction among the plurality of vertical charge transfer electrodes; a horizontal charge transfer path formed at one ends of a plurality of the vertical charge transfer paths for receiving electric charges transferred from the vertical charge transfer paths and transferring the electric charges in the horizontal direction; and an output amplifier formed at one end of the horizontal charge transfer path for amplifying electric charges supplied from the horizontal charge transfer path and outputting to an external, wherein: the pixel in the first pixel column is a first color pixel including a photoelectric conversion element and a first color filer; and the pixels in the second pixel column comprise a second color pixel including a photoelectric conversion element and a second color filer and a third color pixel including a photoelectric conversion element and a third color filer, the second and third color pixels being alternately disposed in the vertical direction and in the horizontal direction, the method comprises: a) a step of reading electric charges from the photoelectric conversion elements to the vertical charge transfer paths by applying a read pulse to two vertical charge transfer electrodes adjacent in the vertical direction among the first to eighth vertical charge transfer electrodes; b) a step of collecting the electric charges read to the vertical charge transfer paths; c) a step of transferring the electric charges from the vertical charge transfer path to the horizontal charge transfer path; d) a step of transferring the electric charges transferred to the horizontal charge transfer path to the output amplifier; and e) amplifying the electric charges supplied from the horizontal charge transfer path and outputting the electric charges to the external.
A patterning precision of a solid state image pickup device, particularly vertical charge transfer paths and vertical charge transfer electrodes, can be mitigated. The patterning precision of a horizontal charge transfer path can also be mitigated. At a given patterning precision, the pixel density can be made higher.
A manufacture yield can be improved. Reliability of solid state image pickup devices can be improved.
With the solid state image pickup device reading method, all pixels of a still image can be read. Moreover, since pixels can be read through thinning, it is easy to read and reproduce a moving image to be monitored.